My questions involve how a 240v fan-forced wall-mounted heating
circuit works when controlled by a single pole thermostat and how to
safely test its line and load wires. I understand that both the feed
white and black wires are hot, and that one of those wires bypasses
the thermostat and feeds directly into the heater while the other wire
connects to the thermostat. This means that the heater always has at
least 110v of juice going into it, whether the thermostat is on or
off. I'm assuming the heater has some sort of electronics that keep it
from running until voltage jumps up from 120v to 240v (when the
thermostat is switched on). Is that right?
I now want to correctly identify which wire is the supply (from the
breaker box) coming into the thermostat and which is the load (going
to the heater). I would like to use my little 2-wire circuit tester
light to do this test. Though only made for 120v 20A circuits I am
assuming I can safely test for the presence of a current by connecting
to either a white or black lead wire and a ground wire, rather than
the other white or black wire (which could potentially also be
carrying a current). Is this assumption correct?
Finally, can someone tell me if its true that there is no circuit (the
flowing in and out of electricity) with these wall mounted heating
units? If both wires going to the heater are sending in current, and
there is no neutral wire returning current, then there isn't a circuit
in the heater. All the juice going to the heater is turned into heat -
there is absolutely nothing to return - therefore no neutral. If
that's the case, then if the heater fails, doesn't that mean that the
entire heater becomes an electrified 240 volt death machine when the
Sorry for the long post - I looked for definitive answers on this
topic before posting but couldn't find any. I need answers to these
questions before I feel comfortable continuing with my project.
yes it does as long as the breaker is closed
There is an potential as long as the t-stat is not closed. (One leg hot)
The potential will shock you and or hurt you. When the stat closes then the
element has enough voltage to start heating.
whether the thermostat is on or
NO electronics, just the resistance of the element.
I have not a clue what you mean by a 2 wire tester light. Most meters have
just 2 wires for testing. It is always better to measure voltage than it is
just for an indication that it is there/on.
If both wires going to the heater are sending in current, and
The neutral has nothing to do with resistance heat unless the unit is 120v.
All the juice going to the heater is turned into heat -
No the element is isolated from the frame or should be. There should also be
an ground conductor that will cause the breaker to trip when or if the
element touches the case.
Seek professional help locally, you may be in over your head.
You're trying to assume something you don't understand. A 120v or a 220v
circuit work in much the same way. A circuit is not just 120v to neutral, a
circuit can also be 120v leg to the other 120v leg, to achieve 220v.
You should read 120v to ground on the unswitched leg, and 120v to ground on the
switched leg only when it is calling for heat. Connecting the 2 legs across the
heater's resistive element is what completes the 220v circuit.
No. The current from each leg is returning through the opposite leg. There is a
circuit. A 220v load is not just any 2 120v lines, they're 2 lines specifically
on opposite legs in your panel.
If the heater fails because the element breaks, each side of the element will
have a 120v potential to ground.
It seems you lack some very basic electrical theory. I suggest you call a
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